The proposed project will examine how nonmarital cohabitation during adolescence and young adulthood causally impacts individual physical and mental health, as well as healthy behaviors that determine future adult health across gender and racial/ethnic groups. The rapid rise in nonmarital cohabitation has markedly changed the landscape of romantic relationships in the United States;cohabitation has become a normative experience for both men and women by age 25. The rapid increase in cohabitation raises concerns about its consequences for the lives of individuals involved in this family form, as research indicates that cohabiters hold lower levels of commitment, and cohabitations are more easily dissolved than marriages. Although the prevalence and patterns of cohabitation have generally been well documented, we know very little about the outcomes of nonmarital cohabitation. This is especially true for young participants;despite the increasing significance of cohabitation at younger ages, the cohabitation literature continues to focus on adults, and treats the experiences of cohabitation the same at all ages. Heterogeneity with age and "meaning" (the goals and purpose of the cohabitation, according to the partners - classifying cohabitation into 4 distinct types) has both been neglected by prior research. A considerable amount of research has established that married individuals live longer, healthier lives than others. Similar research on the parallel health benefits of cohabitation is sparse, and virtually nonexistent from adolescence into young adulthood despite substantial levels of cohabitation at these ages. Our project has three specific aims: 1) Generate descriptive trajectories of an array of health outcomes and behaviors from adolescence into young adulthood separately for men and women and for race/ethnicity, and examine correlations between relationship status (marriage, cohabitation, singlehood) with particular trajectories, using a semi-parametric group-based modeling strategy;2) Use data on relationship histories to model how cohabitation experience causally affects health and healthy behaviors relative to marriage or singlehood from adolescence into young adulthood using longitudinal fixed effects models that control for all unobserved stable characteristics of the individuals;3) Explore how heterogeneity in age (the timing of relationship experience) and in meaning of cohabitation (4 types) alter assessments of the role of cohabitation in health from adolescence into young adulthood. Longitudinal data from the National Longitudinal Study of Adolescents will be used;it is the largest study of adolescents ever conducted, as well as the only one with the means to examine the association between four different types of cohabitation and a variety of health outcomes. PUBLIC HEALTH RELEVANCE: This study will inform programs that target adolescent and young adult health by providing empirical findings about the long-term effects of adolescent romantic relationships (cohabitation and marriage) on mental and physical health and risky behaviors. The project highlights effects of differences in timing and in the type, or meaning, of cohabitation on outcomes (heterogeneity in age and meaning).